Consider the uncontrollable state equation

$$x$($t$)=$

$$

$$

$$

$$

$2100$

$0200$

$0010$

$0001$

$$

$$

$$

$$ x$($t$)+$

$$

$$

$$

$$

$0$

$1$

$1$

$1$

$$

$$

$$

$$ u$($t$)$

Is it possible to find a gain matrix k so that the equation with state feedback u $=$ r $$ kx has eigenvalues

$2,2,1,1?$ Is it possible to have eigenvalues $2,2,2,1?$ How about $2,2,2,2?$ Is the

equation stabilizable?